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A novel approach to SCT dew heaters


philjay
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I did this on my old C11 as I was having alot of dew problems due to the large collector area and dew shields on their own were not much use and stock dew straps just wasted heat by heating the tube and metalwork instead of getting the heat to where it was needed.


 


This together with a large rigid dew shield kept the corrector clear all night even when imaging stuff near the zenith for hours.


 


The heater part is Comax resistance wire which I calculated the length of to give me just a couple of watts I think, very low power with little current draw, cant remember the numbers now but its the principle that matters. The resistance wire was then insulated with heat shrink sleeving and a power lead attached with a bog standard phono plug at the end.


 


I then measured the internal circumference of the corrector flange and cut and bent some microbore central heating tube to suit. This I covered with larger heat shrink and shrank it down to give a nice matt black protective cover.


I threaded the insulated resistance wire through the tube and fixed at both ends with insulated glands which I knocked up on the lathe out of PTFE bar.


 


The heater then sits in the corrector flange in direct contact with the flange. I eventually used a couple of fixing tabs to hold it in place. I also drilled the corrector flange and fitted a grommet so I could feed the heater cable through. The dew shield then had a slot to accommodate the wire and grommet


 


The dew shield was a Homebase plastic swingbin minus top, shortened a little, the base cut out then I built the scope end up with glass fibre to the correct diameter and fitted sticky backed felt so it was a snug push fit


 


It worked well and looked quite professional (apart from the dew shield) and took very little power as the heat was applied close to the place that mattered 


 


Hope its of some use to folks

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